The fundamental steps of processing color light-sensitive materials generally include a color-developing step and a silver-removing step. That is, an exposed silver halide color photographic light-sensitive material is introduced into a color-developing step, wherein silver halide is reduced with a color-developing agent to produce silver and the oxidized color developing agent in turn reacts with a color former to give a dye image. Subsequently, the color photographic material is introduced into a silver-removing step, wherein silver having been produced in the preceding step is oxidized with an oxidizing agent (usually called a bleaching agent), and dissolved away with a silver ion-complexing agent usually called a fixing agent. Therefore, only a dye image is formed in the thus processed photographic material. In addition to the above-described two fundamental steps of color development and silver removal, actual development processing involves auxiliary steps for maintaining the photographic and physical quality of the resulting image or for improving the preservability of the image. For example, there is a hardening bath for preventing the light-sensitive layer from being excessively softened during photographic processing, a stopping bath for effectively stopping the developing reaction, an image-stabilizing bath for stabilizing the image, and a layer removing bath for removing the backing layer on the support.
In general, ferricyanides, dichromates, ferric chloride, ferric ion complex salts, persulfates, etc. are known as bleaching agents. Of these bleaching agents, ferricyanides, dichromates and ferric chloride are good bleaching agents due to their strong oxidizing ability. However, a bleaching solution containing ferricyanides can release poisonous cyanide by photolysis and dichromates including hexa-valent chromium compounds, both causing environmental pollution. Accordingly, the waste processing solution thereof must be made completely harmless by means of special treatment in view of environmental pollution. Also a bleaching solution containing ferric chloride as a bleaching agent is not desirable because materials constituting vessels in which the solution is retained are liable to be corroded due to the extremely low pH and large oxidizing power of the solution. In addition, iron hydroxide is precipitated in an emulsion layer during the water-washing step provided after the bleaching step, resulting in stain formation.
On the other hand, ferric ion complex salts (e.g., aminopolycarboxylic acid-ferric ion complex salts, particularly iron (III) ethylene-diaminetetraacetate complex salts) are employed together with halides (e.g., bromides) in a bleaching solution.
However, ferric ion complex salts have a comparatively small oxidizing ability and, therefore, have insufficient bleaching power. A bleaching solution containing the complex salt as a bleaching agent can attain some desirable objects when bleaching a low-speed silver halide color photographic light-sensitive material containing, for example, a silver chlorobromide emulsion as a major component. However, such a solution fails to fully remove silver due to insufficient bleaching ability or requires a long time to bleach when processing a high-speed, spectrally sensitized silver halide color photographic light-sensitive material containing a silver chlorobromoiodide emulsion or silver iodobromide emulsion as a major component, particularly color reversal light-sensitive materials for photographing or color negative light-sensitive materials for photographing comprising an emulsion containing larger amounts of silver.
Other known bleaching agents than ferric ion complex salts include persulfates. Persulfates are usually used in a bleaching solution together with a chloride. However, this persulfate-containing bleaching solution has less bleaching ability than ferric ion complex salts, thus requiring a substantially long period of time for bleaching.
As described above, bleaching agents which do not cause environmental pollution or corrode vessels and apparatuses have only a weak bleaching ability. Hence, there has been a need to enhance the bleaching ability of a bleaching solution containing a bleaching agent with a weak bleaching ability, particularly a ferric ion complex salt.
In order to perform sufficient bleaching processing using a bleaching solution containing a ferric ion complex salt which has an insufficient bleaching ability, it has been proposed to add various bleach accelerating agents to the processing bath.
Examples of such bleach accelerating agents for bleaching solutions containing a ferric ion complex salt include various mercapto compounds as described in U.S. Pat. No. 3,893,858, Japanese Patent Application (OPI) Nos. 32736/78, 57831/78, 104232/78, 124424/78, 141623/78 and 52534/79, etc.; compounds having a disulfide bond as described in British Patent No. 1,337,346, Japanese Patent Application (OPI) Nos. 95630/78 and 95631/78, etc.; thiazolidine derivatives as described in Japanese Patent Publication No. 9854/78, Japanese Patent Application No. 88938/83 (corresponding to U.S. Ser. No. 612,173 filed on May 21, 1984), etc.; isothiourea derivatives as described in Japanese Patent Application (OPI) No. 94927/78, etc., thioamide compounds as described in Japanese Patent Application (OPI) No. 42349/74, etc.; dithiocarbamates as described in Japanese Patent Application (OPI) Nos. 26506/80 and 20832/77, etc.; and the like.
Of these bleach accelerating agents, however, thioamide compounds and dithiocarbamates have insufficient bleach accelerating effects and therefore, can not achieve the purpose of accelerating a bleaching step. On the other hand, some of the compounds having a mercapto group or a disulfide bond in their molecules, thiazolidine derivatives and isothiourea derivatives have substantially sufficient bleach accelerating effects. These compounds, however, have a large defect in that precipitate is formed in a bleaching solution when color light-sensitive materials are continuously processed in the bleaching solution containing these bleach accelerating agents. Particularly, the above-described precipitate is likely to occur when color light-sensitive materials for photographing comprising an emulsion containing silver iodobromide as a major component and large amount of silver are continuously processed with a low level replenishment or when a reproduced bleaching solution is used.